It is known that a motor vehicle hood is constituted by an outer skin of sheet metal or of plastics material, lined by an internal lining that serves, amongst other things, to increase the stiffness of the hood, in particular in the vicinity of its periphery.
To this end, the lining is generally shaped in such a manner as to co-operate with the hood to form a hollow body that generally follows the outline of the hood.
Stiffened in this way, the hood can be moved without warping excessively.
When the hood is closed, it can be seen that the hollow body often lies over high rigid members that are located in the engine compartment, such as for example: a battery; the flange of a rain tray formed by a scuttle partition; an electronics unit; a pump; a rigid sheath for electric wiring; hinges; a striker plate; etc.
The term “engine compartment” is used to designate the volume underlying the hood and its lining, going from the front of the vehicle as far as the dash panel, in the conventional configuration of a vehicle having a front engine. All of the parts located in this volume are therefore considered as belonging to the engine compartment in the meaning of the invention.
It is also known that hoods are designed to as to inflict as little damage as possible to the head of a pedestrian that impacts against it in the event of a traffic accident. For this purpose, hoods present characteristics for damping impacts in predefined zones.
Nevertheless, because of the presence of the above-mentioned hollow body, the substantially peripheral zone of the hood presents poor characteristics in the face of pedestrian impacts, since the hood is greatly stiffened at its periphery and is therefore not in a position to absorb the energy of an impact with the head of a pedestrian. On the contrary, if the hollow body comes quickly to bear against a high hard point located in the engine compartment, then the pedestrian's head can suffer severe injury by the long-lasting high deceleration to which it is subjected.
The risk of injury for the head of a pedestrian is quantified by calculating an index known as the head injury criterion (HIC) or the head performance criterion (HPC), of value that is well known to the person skilled in the art, and a definition of which can be found in the Dec. 23, 2003 Commission Decision 2004/90/EC relating to technical requirements for implementing Article 3 of the European Parliament and Council Directive 2003/202/EC relating to protecting pedestrians and other vulnerable road users in the event of a collision with a motor vehicle and prior thereto, and amending Directive 70/156/EEC. The deceleration of the head caused by meeting a hard point clearly greatly degrades the HIC.